This invention relates generally to gas turbine engines and, more particularly, to honeycomb seals included in gas turbine engines.
Honeycomb seals are widely used in aircraft, marine and industrial power turbine engines. For example, a gas turbine engine typically includes at least one row of rotor blades and a plurality of honeycomb seals within cavities formed in a rotor assembly. Typically, honeycomb materials having a melting temperature over 2100xc2x0 F., e.g., Hastelloy X, are brazed onto backing plates. During break-in engine operations, seal teeth located on a first rotatable annular member cut grooves or channels into the honeycomb seals located on either a second non-rotatable member or a second rotatable member having a different rotation speed than that of the first rotatable member. The channels cut by the first rotatable annular member with seal teeth define an operating clearance between the seal teeth and the honeycomb material, and permit the honeycomb material to seal against the seal teeth to restrict air from flowing between the cavities formed by the seal teeth and honeycomb material.
During break-in and normal engine operating conditions, the seal teeth cut into the honeycomb material with low incursion rates. High or rapid incursion rates may develop, for example, as a result of tight tolerances. Additional high incursion rates may occur after maintenance is performed to existing turbines and after turbine module components are interchanged or replaced. During operating periods of high incursion rates, frictional heat generated between the seal teeth and honeycomb material increases from a normal operating temperature to a value below that of the melting temperature of the honeycomb material. As a result of the increased temperature, the seal teeth do not effectively cut into the honeycomb material, but rather the honeycomb cells yield and xe2x80x9csmearxe2x80x9d when contacted with the seal teeth. Because the seal teeth do not effectively cut the honeycomb material, a high seal rubbing torque develops and the frictional heat generated between the seal teeth and the honeycomb material is further increased.
The increased temperature induced within the seal teeth causes potential material degradation, possible fatigue cracking and possible quench cracking of the seal teeth. Over time, continued exposure to high temperatures may result in the seal teeth exceeding a yield stress, thus resulting in residual stresses that may reduce fatigue life and degradation of the seal teeth. Furthermore, if the honeycomb material is not positioned a uniform distance from the rotating member blades circumferentially around the turbine, local rubbing may occur. The combination of the local rubbing and the increased temperature of the seal teeth may produce sinusoidal thermal gradients and deeper rubs into the honeycomb material. Furthermore, as a result of the deeper rubs, operating clearances are increased locally, and air may flow between the rotating member and honeycomb material, decreasing an effectiveness of the seal.
In an exemplary embodiment, a gas turbine engine includes a non-rotating assembly including a honeycomb seal that reduces wear to seal teeth disposed within the gas turbine engine. The gas turbine engine non-rotating assembly includes a sealing assembly disposed between rotor components and stator components. The rotor components include a rotatable annular member including seal teeth extending radially outward from the rotatable annular member. The stator components include a non-rotatable member including a honeycomb seal that extends radially inward. The honeycomb seal is fabricated from a material that has a melting temperature less than approximately 2000xc2x0 F.
During engine operations, the rotating seal teeth contact the honeycomb material and generate a temperature that is not greater than the melting temperature of the honeycomb material. Accordingly, as the seal teeth contact the honeycomb material, grooves or channels are cut easily into the honeycomb by the seal teeth. The channels define an operating clearance between the blade seal teeth and the honeycomb material, and permit the honeycomb material to seal against the seal teeth to restrict air from flowing between the seal teeth and honeycomb material. Because the melting temperature of the honeycomb seal is less than 2000xc2x0F., a temperature increase generated when the rotating seal teeth cut into the honeycomb seal is limited to a temperature less than the melting temperature of the honeycomb material. Furthermore, because the melting temperature of the honeycomb material is less than 2000xc2x0 F., the temperature increase induced within the seal teeth is reduced in comparison to temperature increases induced in seal teeth cutting through known honeycomb seals fabricated from materials with higher melting temperatures. As a result, property degradation to the seal teeth and cracking due to thermal stresses are reduced.